Currently available implementations of head-related transfer function (HRTF) filters are extremely computation expensive and require a large amount of memory for storing filter coefficients. This invention solves both problems and still provides additional advantages resulting from its flexibility.
An important feature of most DVD players and home theater systems is their ability to provide a more realistic sound experience than is possible with conventional stereophonic systems through the use of multi-channel audio. Some systems employ 5, 6 or more audio channels plus an additional low frequency extension (LFE). However, the cost of multi-speaker systems has created the need to simulate multi-channel audio using conventional stereophonic systems. This is done by virtual surround systems, which employ algorithms that try to localize sounds in virtual space using head-related transfer functions (HRTFs). Other situations may pose further restrictions related to computational cost and memory, making it difficult to implement virtual surround systems. In these cases, there is a need for an algorithm that creates a wider sound image by processing only two channels of audio. This is called stereo enhancement. Stereo enhancement can also improve the sound quality of conventional stereo music, particularly of early recordings with excessive inter-channel separation or extremely narrow sound image. The problem to be solved consists of processing a conventional stereo signal to create a wider sound image by using 3D audio techniques.
Current methods for stereo enhancement show undesirable artifacts such as spectral coloring and weakening of vocals. Spectral coloring usually occurs as a consequence of the use of HRTF filters for spatial localization. Weakening of vocals is a consequence of the manipulation of the amount of correlation between left and right channels. Conventional virtual surround systems use only HRTF filters to achieve virtual sound localization.
The prior art includes a number of virtual surround systems using HRTF to localize sounds in virtual space requiring either 2 loudspeakers or headphones. However, these systems encounter a number of technical limitations. For example an HRTF may vary considerably from person to person. Real listening rooms have unpredictable shapes and furniture layout causing unwanted reflections. Some prior art systems use head-mounted speakers and others try to increase robustness by modulating auditory cues.